.OST is a Microsoft Windows file type associated with Microosft Outlook; part of the Microsoft Office product suite. This file is generated by the application for the purpose of storing the content of the user's mailbox on the local hard drive for offline use. In Office XP and earlier versions, the OST file will become corrupt if its size grows to over 2 gigabytes, generally causing Outlook to freeze up in use or while starting up. Reducing the size of the mailbox and manually deleting the file is the solution for this condition (a new file is created automatically the next time the program is started). Office 2003 features a new format for the file with support for a 20 gigabyte working file size.
OST is the abbreviation for Officer Safety Training in Law enforcement in the United Kingdom . This covers self-defence, is given to all UK Police Officers as part of their initial training and all officers must pass regular OST updates and tests during their careers.
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